Method and device for recognizing combustion in a particle filter

ABSTRACT

The invention relates to a method for recognizing combustion in a particle filter ( 6 ) provided in the exhaust line of a combustion engine ( 1 ), the filter ( 6 ) having periodic regeneration that is controlled by suitable means, which comprises a step of measuring or estimating parameters representing combustion in said filter ( 6 ) and a step of processing said parameters to diagnose a combustion instance and estimate the strength thereof, and characterized in that said steps are implemented during the entire phase of engine operation ( 1 ), and particularly outside the phases of regeneration controlled by the filter ( 6 ). The invention also relates to a device capable of implementing such a method.

The present invention claims the priority of French application 0853563filed on May 30, 2008 the content of which (text, drawings and claims)is incorporated here by reference.

The invention relates to the field of pollution control of internalcombustion engines, and more specifically the control of particlefilters installed in the exhaust line of the engines, in order to trapthe particles emitted by the combustion in the engine.

During its operation, an internal combustion engine produces exhaust gasoriginating from the combustion of fuel and containing a certain numberof regulated pollutants. The pollutants emitted by the combustion of anengine can contain solid carbonaceous particles. Failing to calibratethe engine so that it emits only the permissible quantity of regulatedpollutants, the exhaust gas must undergo a treatment in order to reducethese pollutants to a level lower than the normalized thresholds.

The gas treatment device is in general situated in the exhaust circuitof the engine. This is called post-treatment of gas. This treatmentdevice can consist of one or more elements and can comprise inparticular a particle filter.

An automotive particle filter eliminates by filtration the solidparticles present in the exhaust gas of engines, generally dieselengines. Once trapped inside the filter, the particles must beeliminated periodically by raising the temperature inside the filterfrom 450° C. to 700° C. in order to cause their combustion. Thisoperation is usually called “regeneration” of the particle filter.Traditionally, the energy necessary for regeneration is supplied bycontrolled increase of the exhaust gas temperature.

Traditionally during the regeneration phases, the energy surplus at theexhaust necessary to raise the temperature relative to the normaloperation of the engine is supplied by post injections, in other wordsdelayed fuel injections, after the high dead point of the cycle, or bydegradation of the combustion yield, or by direct fuel injection in theexhaust line.

In case of post injection, the injection can burn completely orpartially in the engine, generating an increase of the exhaust gastemperature, or if the injection is sufficiently delayed, induce anincrease of the quantity of CO and HC at the exhaust, which oxidize whenthey arrive at the oxidizing catalyst in order to generate heat. It isthis last phenomenon which also plays a role if fuel is introduceddirectly in spray or vapor form in the exhaust line of the engine.

However, the carbonaceous particles trapped by the filter arecombustible material, and their combustion can be self supporting beyonda temperature of approximately 450° C. if the filter employs an additiveto facilitate regeneration, and 600° C. if not, and from the time thatan oxidizer is available in sufficient quantity.

Since oxygen is always present in the exhaust gas of engines, thecombustion of soot particles can start if the filter is significantlyloaded with soot particles, leading to a significant release of energyin the filter, which can cause damage to the filter (for instancecracking) or its destruction.

Significant soot loading of the filter can be observed when theautomotive vehicle equipped with the filter operates mainly in so-calledurban driving, in other words at low speed and with frequent stops. Inthese conditions, it is extremely difficult to regenerate a particlefilter, because the exhaust gas is far away from the regenerationtemperature of the filter, or it reaches only a temperature high enoughto trigger regeneration during a time interval which is too short tocomplete this regeneration. Typically, the exhaust gas temperature of anautomotive diesel engine supercharged with a turbo compressor, andmeasured at the outlet of the turbine of the turbo compressor, is in theorder of magnitude of 150° C., and minimum 450° C. is required to startregeneration of a filter with additives.

In other respects, if after extreme soot loading of the particle filter,the engine is subjected to prolonged operation under heavy load, thetemperature of the exhaust gas can trigger spontaneous combustion ofsoot in the filter. In certain circumstances, the combustion of sootwhich started prior to the shut-down of the engine can continue afterits shut down, and even initiate shortly after the shut-down, if theexhaust circuit is particularly hot and the filter is no longer cooledby the exhaust gas flow.

These uncontrolled combustions of soot can damage the filter, if theyoccur at high temperature or if they provoke a too rapid increase of thetemperature in the filter. Such damage is detrimental for more than onereason. On the one hand, the efficiency of the post treatment systembecomes questionable, and on the other hand, according to actualregulations and for on board diagnostics (“OBD” function), it isnecessary to guarantee the efficiency of post treatment systems for thelifetime (typically 160,000 km according to EURO 5 standards) or toalert the driver of the vehicle in case of failure of the post treatmentsystem.

Patent FR2814498 of Renault S. A. discloses means for diagnosing thefailure of a particle filter or for calculating its loading by observingthe energy released during regeneration of the filter. Although it isknown how to control the regeneration of a particle filter throughvarious strategies, prior technology does not know a method aimed atcontrolling the occurrence of this type of spontaneous combustion ofparticles in the filter, and the filter failures that they can generate.

Furthermore, the effect of this type of uncontrolled combustion ofparticles on the soot loading of the filter is actually not taken intoaccount in the models for determining the loading.

The goal of the present invention is to propose a method for recognizinga combustion, and specifically an uncontrolled combustion, in a particlefilter installed in the exhaust line of a combustion engine. Thisrecognition and characterization of the detected combustion allow todiagnose a failure of the filter or to take into account the effect ofthis combustion on the soot loading of the filter, and this during thewhole operational phase of the engine. The invention allows to controlthe filter during all its utilization phases, and not only during itscommanded regenerations as known in prior technology.

To this end, the proposed method comprises a step of measuring orestimating the representative parameters of a combustion in the filterand a step of processing these parameters in order to diagnose theoccurrence of a combustion and to determine the intensity of it, amethod in which these steps are implemented during the whole operationalphase of the engine and in particular outside the commanded regenerationphases of the filter, and in one variant, also during a predeterminedtime following the shut-down of the engine.

By preference, the considered representative parameters are respectivelythe temperature at the inlet of the particle filter and the temperatureat the outlet of the particle filter.

The estimation or measurement of these parameters and their processinghave therefore as originality of being performed also outside the phasesof commanded regeneration of the filter. Furthermore, estimating,measuring and processing of the considered parameters are continuedafter engine shut down.

With this kind of method, the conclusion can be made that anuncontrolled combustion of particles occurred in the particle filter (6)if the temperature at the outlet of the filter (6) exceeds thetemperature at the inlet of the filter by a predetermined margin for apredetermined time, while the engine control module does not command aregeneration.

In a variant, the temperature gradient in filter (6) is estimated basedon the evolution of the temperatures at the inlet and outlet of thefilter, and the conclusion is made that a combustion of particlesoccurred in particle filter (6) if the estimated temperature gradient isgreater than a predetermined maximum.

When the occurrence of a combustion in the filter is detected, thequantity of soot burned during this combustion can also be evaluatedbased on the evolution of inlet and outlet temperatures of the filterduring this combustion and based on the duration of this combustion.

The proposed method can serve as failure diagnostic of a particle filterinstalled in the exhaust line of a combustion engine. Indeed, failure ofthe particle filter is detected if the temperature downstream of thefilter exceeds the temperature upstream of the filter by a predeterminedvalue during a predetermined time.

The conclusion is also made that failure of the filter occurred if theobserved temperature gradient exceeds a predetermined limit.

In the framework of a vehicle with internal combustion engine equippedwith an exhaust line comprising a particle filter, and also equippedwith “on board diagnostics” (OBD) module, the particle filter failureinformation can be entered in the module if a failure of the particlefilter is detected.

Furthermore, if the vehicle contains an illuminated warning device foranomaly of the particle filter, for instance inside the cabin, theilluminated device is activated if a failure of the particle filter isdetected in order to alert the user of the failure.

The invention relates also to a device for implementing the describedmethod. This device comprises an internal combustion engine equippedwith an exhaust line comprising a particle filter, means for commandingthe regeneration of the filter, means for estimating the representativeparameters of a combustion inside the particle filter, means forprocessing these parameters in order to diagnose the occurrence of acombustion and for estimating its intensity, and is characterized inthat said means is periodically activated during the whole operationaltime of the engine, and not only during the controlled regenerations ofthe filter as is the case in prior technology.

By preference, the device is equipped with means for estimating or meansfor measuring the temperature at the inlet of the particle filter, and atemperature probe at the outlet of the filter.

The invention is described in more detail here after and with referenceto the unique figure representing schematically a device forimplementing the method according to a preferred implementation mode.

FIG. 1 represents schematically the assembly consisting of an internalcombustion engine and its main air loop, in other words its intake andexhaust circuit, and means for post treatment of the exhaust gas, andthe devices necessary for implementing the diagnostics strategy of theparticle filter according to the preferred implementation mode of theinvention.

A diesel engine 1 is supercharged by means of turbo compressor 2. Theadmission of air in the engine takes place via inlet line 3. The exhaustof gas after the combustion takes place via exhaust line 4.

In the example shown here, the post treatment of exhaust gas involves anoxidizing catalyst 5 and a particle filter 6.

The engine control module 7 (here shown as an assembly, but can consistof several elements or can be divided in multiple boards or electronicboxes) controls the various command strategies of the engine, the fuelinjection strategy, and controls the post treatment means, and inparticular monitors the filling of the particle filter. Processor 7 alsointegrates the command means suitable for commanding the periodicregeneration of particle filter 6. The engine control module 7 comprisesalso an OBD function (On Board Diagnostics) 8 which catalogs and recordsthe main operational failures or anomalies of the engine and itsperipheral equipment, and can trigger, for instance, a warning in caseof dysfunction, in the form of an illuminated device 9 warning theoperator of the engine or the driver of the vehicle equipped with it.

In the preferred implementation mode shown here, a temperature probe 10is located in the exhaust line 4 between the oxidizing catalyst 5 andthe particle filter 6, at the entrance of the particle filter 6. Atemperature probe 11 is located in the exhaust line 4 at the exit of theparticle filter 6.

Note that the temperature probe 10 at the entrance of the filter can bereplaced easily by a digital model for estimating the temperatureupstream of the particle filter, which is stored in the engine controlmodule. This variant offers a certain cost advantage, at the price of areduced accuracy, but nevertheless remains compatible with traditionalautomotive practice.

Temperature probe 10 at the entrance of filter 6 and temperature probe11 at the exit of filter 6 communicate with engine control module 7, forinstance through the intermediary of bus 12 and 13, the control moduleintegrates moreover the proposed process. Overall, the developed processconsists in comparing the temperature upstream and the temperaturedownstream of the particle filter 6, as well as the evolution of thesetemperatures, during the operation of engine 1 and during apredetermined time, for instance of one minute, after engine shut down.Therefore, the temperatures are not only compared during theregenerations of filter 6 triggered by the engine control module.

By monitoring these two temperatures and their evolution, the proposeddiagnostics allows, on the one hand, recognition of spontaneouscombustions in particle filter 6, and on the other hand, diagnosis ofthe degradation of filter 6 due to too intense or too rapid release ofenergy.

Typically, if the temperature measured by the probe at the exit of thefilter 11 exceeds the temperature of the probe at the entrance of filter10 by a certain margin during a certain time, while the engine controlmodule 7 does not command a regeneration (for instance by post injectionof fuel), the strategy concludes that an uncontrolled combustion of sootis taking place in filter 6. These temperature and time thresholds allowthe discrimination between a combustion in filter 6 and a reduction ofthe load of engine 1, which results in less hot exhaust gas, which infunction of the thermal inertia of the filter can result temporarily inthe temperature measured by probe 10 being below the temperaturemeasured by probe 11. It is easily understood that the temperaturethreshold and the time in question depend on the employed filter andengine and the operating points authorized by the engine control module.

In addition, the temperature gradient in the filter can be estimated bymonitoring the temperatures at the entrance and the exit of filter 6. Ahigh temperature gradient is a good indicator of an uncontrolledcombustion in filter 6.

By detecting the uncontrolled combustion, and observing the temperaturesupstream and downstream of the particle filter and their evolutionduring this spontaneous combustion, the estimated loading level inparticle filter 6 can be corrected, taking into account the quantity ofoxidized particles during the uncontrolled regeneration.

Besides, whether we are dealing with commanded or uncontrolledregeneration of the particle filter, by comparing temperatures upstreamand downstream of filter 6 the conclusion can be made that filterdegradation occurred. If the temperature measured by probe 11 exceedsthe temperature of probe 10 by a certain value (potentially differentfrom the threshold used for detection of an uncontrolled combustion)during a certain time (potentially different from the time used for thedetection of a spontaneous combustion), the conclusion is then that adegradation of the filter took place.

Similarly, if the estimated temperature gradient in filter 6 is greaterthan a predetermined maximum, the conclusion is that a degradation ofthe filter took place.

If the strategy concludes that a degradation of the filter took place,the OBD module 8 of engine control module 7 is then warned. Inaccordance with existing and future regulations, the information can beentered in a memory of engine control module 7 or of OBD module 8, andan illuminated failure device 9 warns the driver of the encounteredanomaly.

In the framework of an automotive application and in conformance withactual and future regulations, which impose for instance monitoring ofthe effectiveness of the filtration of the filter over 160,000 km in theframework of European standard EURO 5, it becomes possible to alert theuser that a critical regeneration of the particle filter, eithercontrolled or uncontrolled and eventually spontaneously triggered byvehicle driving conditions, was detected and that its performance couldbe degraded.

1. A method for recognizing a combustion in a particle filter installedin an exhaust line of an internal combustion engine and wherein theperiodic regeneration of the particle filter commanded by appropriatemeans; the method comprising a step of measuring or estimating therepresentative parameters of a combustion in the particle filter and astep of processing these parameters in order to diagnose the occurrenceof a combustion in the particle filter and to estimate the intensity ofthe combustion; said steps of measuring or estimating and processingbeing implemented during the whole operational phase of the engine, andin particular outside the commanded regeneration phases of the filter.2. The method according to claim 1, wherein said steps of measuring orestimating and processing are implemented during a predetermined timefollowing shut-down of the combustion engine.
 3. The method according toclaim 1, wherein said representative parameters are the temperature atthe inlet of the particle filter and the temperature at the outlet ofthe particle filter.
 4. The method according to claim 3, wherein aconclusion is made that a combustion of the particles in the particlefilter took place if the temperature at the outlet of the particlefilter exceeds the temperature at the inlet of the particle filter by apredetermined margin during a predetermined time.
 5. The methodaccording to claim 3, characterized in that the temperature gradientinside particle filter is estimated based on the evolution of thetemperatures at the inlet and outlet of the filter, and that aconclusion is made that a combustion of the particles in the particlefilter took place if the estimated temperature gradient is greater thana predetermined maximum.
 6. The method according to claim 1, whereinwhen a combustion inside the particle filter is detected, the quantityof soot burned during the combustion is evaluated based on the evolutionof the temperatures at the inlet and outlet of the particle filterduring the combustion and based on the duration of the combustion.
 7. Amethod for diagnosing the failure of a particle filter installed in theexhaust line of an internal combustion engine employing a method forrecognizing a combustion according to claim 2, wherein a conclusion ismade that the particle filter failed: (a) if the value of thetemperature at the outlet of the particle filter exceeds the temperatureat the inlet of the particle filter by a predetermined value during apredetermined time; or, (b) if the estimated temperature gradient of theparticle filter is greater than a predetermined limit.
 8. (canceled) 9.The method according to claim 7, wherein the combustion engine andparticle filter are part of a vehicle; the vehicle comprising an “onboard diagnostic” (OBD) module, the method further including a step ofentering information of failure of the particle filter in the OBD moduleif a failure of the particle filter is detected.
 10. The methodaccording to claim 7, wherein the combustion engine and particle filterare part of a vehicle; the vehicle comprising an illuminated warningdevice for warning of an anomaly of the particle filter, said methodfurther including a step of activating said illuminated warning if afailure of the particle filter is detected.
 11. A device comprising acombustion engine equipped with an exhaust line comprising a particlefilter, means for commanding the regeneration of said particle filter,means for estimating the representative parameters of a combustion inthe particle filter, means for processing these parameters in order todiagnose the occurrence of a combustion and to estimate its intensity,characterized in that said means are employed during the wholeoperational phase of the engine, and in particular outside the commandedregeneration phases of the particle filter.
 12. The device according toclaim 11, wherein the estimating means of the parameters are means forestimating or measuring the temperature at the inlet of the filter and atemperature probe at the outlet of the particle filter.